1. Field of the Invention
Embodiments of the present invention relate to diphenyl anthracene derivatives, and to an organic electroluminescent device using the same. More particularly, embodiments of the invention relate to diphenyl anthracene derivatives that are useful as blue electroluminescent compounds, and to an organic electroluminescent device using the same that offers improved efficiency, driving voltage and luminance.
2. Description of the Related Art
An organic electroluminescent (organic EL) device is an active drive type emission display device that operates under the principle that when current is applied to fluorescent or phosphorescent organic compound layers (hereinafter xe2x80x9corganic layersxe2x80x9d), electrons and holes are combined in the organic layers to then electroluminesce. Organic electroluminescent devices have various advantages including being lightweight, simple components, having a simplified fabrication process, and offering a wide range of colors with high luminescence. Also, organic EL devices can enable moving picture display perfectly with high color purity, and the devices have electrical properties suitable for portable electronic devices at low power consumption and low driving voltage.
Such organic EL devices typically can be classified into low molecular weight organic EL devices and polymer EL devices, depending on the materials used to manufacture the devices.
Low molecular weight organic EL devices have advantages, including being simple and easy to synthesize and purify to a high degree of emissive compounds, and three primary color pixels can easily be obtained. However, since organic layers typically are formed by vacuum deposition, low molecular weight organic EL devices are difficult to be suitably applied for large-screen size processes, which typically use a spin coating method or an ink jet printing method. Therefore, in order to apply the low molecular weight organic EL devices for practical applications, there is still room for improvement in quantum efficiency and color purity, and there remains a need to prevent crystallization of thin layers.
In order for low molecular weight organic EL devices to exhibit high-efficiency, high-luminance emission properties, they typically must have a multiple-layered structure of organic layers, including a hole injection layer, a hole transporting layer, an electron transporting layer, a hole blocking layer, etc. Such organic layers should be stable thermally and electrically during operation of the device because when a voltage is applied, thermally unstable molecules having low morphological stability are rearranged due to heat generated at the device, resulting in local crystallization and lowering of emission efficiency, thereby shortening the useful life of the device.
Research on polymer EL devices has been accelerated since the discovery of the ability of poly(1,4-phenylene vinylene) (PPV), xcfx80-conjugated polymer, to emit light when exposed to electricity. xcfx80-conjugated polymers have an alternating structure of single bonds ("sgr"-bonds) and double bonds (xcfx80-bonds), where xcfx80-electrons are evenly distributed to be freely movable in the polymer chain. Accordingly, xcfx80-conjugated polymers have semiconducting properties and can emit light of a visible range corresponding to the HOMO (highest occupied molecular orbital)-LUMO (lowest unoccupied molecular orbital) energy bandgap, via proper molecular designing, when applied to an emissive layer of an EL device. Such a polymer can be formed as a thin layer by spin coating or printing during the manufacture of EL devices, so that the EL device can be fabricated in a simplified manner and can easily be used in making a large-screen size at low costs. However, such polymer EL devices have lower emission efficiency than low molecular weight EL devices, and they experience shortened lifetime characteristics due to deterioration of emissive polymer. Since defects that promote deterioration in molecular chains are generated during synthesis of such polymer materials, and impurities are difficult to refine, it is difficult to obtain high-purity materials.
To address the problems of polymer EL devices while having advantages of both polymers and low molecular weight materials, there is demand for development of new materials.
The description herein of various disadvantages associated with known materials, methods, and apparatus is in no way intended to limit the various embodiments of the invention. Indeed, certain embodiments of the invention may include one or more known materials, methods, apparatus, without suffering from the disadvantages described herein.
Various embodiments of the present invention provide diphenyl anthracene derivatives free of molecular defects, having improved thermal stability and crystal stability, that are easily purified, and easily capable of forming a thin layer using a soluble solvent. Embodiments of the present invention also provide an organic EL device with improved luminance, driving voltage and emission efficiency by employing the diphenyl anthracene derivatives.
In accordance with a feature of an embodiment of the present invention, there is provided a diphenyl anthracene derivative represented by the following formula: 
wherein R1 and R2 are independently a hydrogen atom; a C1-20 linear or branched alkyl group; a C5-20 cycloalkyl group; a C6-20 aryl group; a C4-20 heteroaryl group; or a C6-20 aryl group having at least one substituent selected from the group consisting of a halogen atom, a C1-10 halogenated alkyl group, xe2x80x94Si(R)(Rxe2x80x2)(Rxe2x80x3), a C1-10 alkyl group, a C1-10 alkoxy group, a C6-10 aryl group, a C4-10 heteroaryl group and xe2x80x94N(R)(Rxe2x80x2),
Ar1, Ar2, Ar3 and Ar4 are independently a hydrogen atom; a C1-20 linear or branched alkyl group; a C5-20 cycloalkyl group; a C6-20 aryl group; a C4-20 heteroaryl group; or a C6-20 aryl group having at least one substituent group selected from the group consisting of a halogen atom, a C1-10 halogenated alkyl group, xe2x80x94Si(R)(Rxe2x80x2)(Rxe2x80x3), a C1-10 alkyl group, a C1-10 alkoxy group, a C6-10 aryl group, a C4-10 heteroaryl group and xe2x80x94N(R)(Rxe2x80x2), where at least one selected from the group consisting of Ar1 and Ar2, and Ar3 and Ar4 can be interconnected, respectively, and R, Rxe2x80x2 and Rxe2x80x3 are independently selected from the group consisting of a hydrogen atom, a C1-10 alkyl group, a C1-10 alkoxy group, a C6-10 aryl group and a C4-10 heteroaryl group.
In accordance with another feature of an embodiment of the present invention, there is provided an organic EL device comprising an organic layer positioned between a pair of electrodes, the organic layer containing the above-mentioned diphenyl anthracene derivative.